Riboflavin transport by rabbit kidney slices: characterization and relation to cyclic organic acid transport

The transport of riboflavin and the relationship of riboflavin transport to the transport of the cyclic organic acids, aminohippurate and penicillin, were investigated in small renal slices in vitro. Riboflavin was accumulated by rabbit renal slices by a transport system that was inhibited by sugar-containing and sugarless flavins, cyclic organic acids including aminohippurate and penicillin, dinitrophenol and cold temperatures, but not by D-ribose or the weak base tolazoline. The transport of riboflavin into renal slices was not solely due to intracellular binding or metabolism of the riboflavin. Aminohippurate, penicillin and riboflavin inhibited the active accumulation of [14C] aminohippurate and [14C]penicillin by kidney slices. These studies support the notions that: 1) riboflavin is accumulated in kidney cortex slices by an energy-dependent saturable transport system; 2) riboflavin accumulation by kidney slices is inhibited by cyclic organic acids and sulfhydryl reagents, but not weak bases; and 3) riboflavin is a competitive inhibitor of aminohippurate as well as an inhibitor of penicillin G accumulation by kidney slices.